Speed control of electric machines



1953 J. M. PESTARINI ,660,

SPEED CONTROL OF ELECTRIC MACHINES Filed Sept. 25, 1948 2 Sheets-Sheet 1 INVENIDR.

1953 J. M. PESTARINI SPEED CONTROL OF ELECTRIC MACHINES 2 Sheets-Sheet 2 Filed Sept. 25, 1948 INVENTOR.

Patented Nov. 24, 1953 UNITED STATESw lTENT QFFIQE This invention relates to alternating current machines rotati -.g at a speed difierent from the speed correspor lg to their synchronous speed.

It is often des "d to have alternating machines with their shaft rotating at a speed difierent from the one corresponding to the synchronous speed relative to the frequency of the currents supplying the machine with energy, say through its stator winings. Such a result may be obtained by supplying the rotor with a polyphase system of windings fed by an auxiliary alternating current source or an adequate frequency. In this case the absolute rotational speed of the shaft will be the algebraic sum of the absolute rotational speed of the magnetic fiel created by the current traversing the stator windings and the relative rotational speed of th field created by the currents of the rotor windings with respect to the said rotor.

' his invention discloses means controlling the "frequency of the auxiliary alt rnating polyphasc currents and their amplitude.

Such means consists essentially in a regulator dynamo rotating at a speed proportional to the absolute speed of the shaft and able to supply a current, varying very quickly for small speed variations from the desired value and after amplification, driving the auxiliary alternating current generator which energizes the rotor windings of the main machine.

The auxiliary alternating current generator, supplying the rotor of the main machine with an auxiliary system or polyphase currents, may he an alternator. In this case the auxiliary systern of currents has a current intensity which decreases c rly towards zero when the frequency of said auxiliary system of currents decreases towards zero, leaving the rotor of the main insufficiently excited for low values of said frequency and not excited at when said -irequency becomes zero. This invention discloses special generators creating currents, the intensity of which is independent of their fre quency, and which become direct currents of a predetermined intensity when the frequency becomes zero.

Two kinds of auxiliary alternating current generators of the latter type are disclosed in this invention, the first one essentially consisting of a circular rheostat upon which a polyphase system of sliding contacts move, collecting a polyphase system of currents; the second variant consists in a polyphase system of brushes sliding along the commutator of an auxiliary dynamo having its armature rotating with respect to its field inductor.

8 Claims. (Cl. 318-19'7) The thus obtained auxiliary alternating currents are generally amplified preferably by means of amplifying metadynes, one inetadyne being used for each phase of the auxiliary polyphase system.

Some examples of application 01" this invention are given below, references being made to the accompanying drawings.

Figure 1 gives the complete scheme with the auxiliary alternating current generator or the kind comprising a, circular rheostat; Figure 2 shows the variant for which the auxiliary generator is an alternator; Figure 3 gives a view of the auxiliary alternating polyphase generator being a dynamo with a polyphase system of slidbrushes; Figure 5 gives a scheme for the amplification of the auxiliary alternating polyphase currents; Figure 4 shows an improvement of the regulator dynamo,

In Figure 1, two main machines 1 and 2 are indicated directly coupled on the same shaft. The machine I is an alternating current motor having its stator fed through its terminals l5 by a three phase current source not shown. its rotor is indicated bearing a polyphase winding traversed by currents carried through the slip rings 35. The machine l is adapted to drive machine 2 which is any desired load creating device, at a predetermined speed.

A regulator dynamo 3 is coupled on the same shaft as the main machines. Said regulator dynamo is provided with a shunt field winding t and connected to a battery 2? through low re sistance windings 5, iii. A rheostat 22a is inserted. in the circuit or the field winding l for setting the resistance of said circuit.

While a conventional dynamo supplying direct current is set to operate with its magnetic circuit substantially saturated in order to reach stability of operation, a regulator dynamo is set to operate with its magnetic circuit unsaturated the resistance of its excitation circuit is set at such a value allowing for a rapid variation of the armature current close to its limit of stability.

In order to obtain an operation at the very limit of stability of the current, the conductance which is the inverse of the resistance, of the circuit in which the main field winding t is insertet is set through the rheostat 22a to be equal to the ratio of the exciting current traversing the field winding 45 to the electromotive force induced by the armature of the regulator dynamo 3 when the absolute rotational speed of the shaft has a desired value, the magnetic circuit of the regulator dynamo 3 being completely unsaturated. Under these conditions, the regulator dynamo .3 will supply or absorb a current which varies very quickly for even slight departures from the desired value of the speed of the shaft.

The regulator dynamo and its action has been described in many previous patents, see Patent 1,oe2,o3o. Its main excitation may be a shunt or so "ies excitation.

The current supplied or absorbed by the regulator dynamo, referred to as regulator current, traverses the variator winding $3 of an amplifying inetadyne ii supplying though its secondary brushes 1) and 02 current to the armature of an auxiliary dynamo 'i which is separately excited by the field winding ti connected to the direct current source 21.

The regulator current of even very small intensity is amplified through the amplifying nietadyne to any desir d value for supplying the auxiliary dynamo 'l with the current necessary to this dynamo to drive, by means of the shaft iii, a use of contacts I9, 2i s along a circular re istor l8 at two opposite points and 26 by direct current supplied by battery 2! and of intensity set through the rheostat 50.

The amplifying n'ietadvne has been described in United Fatent 2,112,60 l March 29, 1938.

The amplifying inetadyne may be provided with an anti-hunting member in the form of winding connected across the secondary wind ing or" a transformer the primary of which is inserted. into the armature circuit of the auxiliary driving dynamo i. The action of this anti.- hunting means is clearly expla ned in the United States Patent 2,203,544, June 4. 1946. Similarly, the secondary compensating or hypo-compen ating winding 55 is connected between secondary brush b of nictadyne i and the are ature of dynamo The action of this windin. s clearly explained the British Patent 4:20,.16'7, Nor eon ber 1934.

The aiuriliary alternating currents collected by means of tho aiding contacts i9, 23G, 21 and 252 supplied to the secondary windings 23 and 24 of the amplifying metadynes it and i4 respectively. The inetadynes it it supply alternating current through their secondary brushes h and d to the rotor of the main machine l by n: of sliprings 35.

In order to increase the sensitivity of the regulator dynamo to the speed variations of its shaft, an auxilier, series connected field excitation may be provided for compensating a part of the ohrrc drop of the external circuit of the regulator dynamo. A further improvement of the regulator dynamo schematically indicated by r gure t where pair of main brushes H and if for collecting the main current absorbed or supplied by the regulator dynamo are connected to the main terminals l'i'a, i'ib which are adapted to connected. to inetadyne winding I3 shown in l' The en .iiary brushes lilo, and Iflb are connected to the shunt field excitation 4. This arrangement allows for the field shunt excitation current to be independent from the variable crush voltage drop that occurs under the main brushes it and I l. The setting resistor 22a is indicated inserted in the circuit of the shunt field excitation t.

In many applications it is desired to vary the of the shaft of machine 5 and this is easily obtained by varying the resistance of the resister 22c inserted. in the circuit of the field wind in? of the regulator dynamo. The actuating means of the resistor 22a may be operated by hand or automatically in response to predeter mined operational characteristics of the system.

It is important to notice that the intensity of the auxiliary polyphase system of currents feeding the rotor of the main machine l is practically independent from the value of the frequency of the said currents and depends only on the setting of the resistor 50. Thus when the frequency of the auxiliary polyphase alternating currents is zero, the rotor of the main machine I is fed by a system of direct currents, the amplitude of which depends solely on the setting of the resistor 50.

Polyphase currents may be supplied to the machine I by means of a dynamo 49 as indicated by Figure 3. The armature of the dynamo is driven by the shaft and rotates with respect to its field inductor 43. A system of angularly displaced polyphase brushes 59, 60, 5| and 62 rotatably contact the commutator Me of the dynamo 49. The brushes 5%, Ell, 62 are mounted on the shaft 55 by the auxiliary dynamo l of Figure l. The polyphase system of currents collected through the above mentioned polyphase system of brushes is carried through the sliprings 60, 70, I! and T2 for supply to the windings 23, 24 of the metadynes i4, it, as previously described.

When the polyphase system of brushes 58, 60, 6!, G2 is at rest, and the regulator current is zero, the rotation of the dynamo armature through shaft 35, provides direct currents collected by the polyphase system of brushes are supplied to metadynes M, 16. The amplitude of such direct currents depends on the setting 01' the resistor 56a inserted in the circuit of the field winding of the dynamo 49. The said resister controls the amplitude of the auxiliary alternating polyphase currents independently from their frequency when the shaft 51 is rotating.

Figure 2 shows a variant arrangement. The two main machines 1 and 2 are directly mechanically coupled to the regulator dynamo which is shunt excited by its field winding t and connected to a direct current source which takes the form of a shunt excited saturated dynamo l I. The regulator current trave'ses the secondary variator winding 13 of an amplifying inetadyne 9, the secondary brushes b, d which energize the field excitation I. of an auxiliary dynamo l. The armature of the latter is energized by a constant current supplied by the amplifying metadyne S, the intensity of which is determined by the value of the current traversing the secondary variator winding l2 and being set by a resistor in series therewith.

The auxiliary dynamo 1 drives an auxiliary alternator it which in its turn supplies a system of auxiliary alternating polyphase currents to the rotor of the main machine I through the sliprings 35.

The value of the speed of the common shaft connecting main machines I and. 2 may be much fled by setting the resistor 22a inserted in the circuit of the field winding of the regulator dynamo may be made by hand or automatically in response to variations in the operational characteristics of the system.

The auxiliary alternating polyphase currents supplied by the alternator it are generally amplified preferably by means or amplifying metadynes. One metadyne being used for each. phase of the polyphase system as indicated by Figure 5 The modification of the resistor 22a where each of the three phase currents supplied by the alternator l traverses the secondary variator windings 39, t0 and 41 respectively of the amplifying metadynes 9'5 and ti; respectively. The latter are driven by a motor The amplifying metadynes have been generally indicated in their simplest scheme but they may be provided with anti-hunt and compensating windings as previously described.

The scheme of Figure 2 does not allow for the excitation of the rotor of the main machine i when the regulator current is zero. Therefore this scheme can be applied oniy when the speed of the shaft must be always different from the synchronous speed corresponding to the frequency of the terminals is. On the contrary, the schemes involving the circular resistor 19 with a sliding polyphase system of contacts or the auxiliary dynamo d9 of Figure 3 with a sliding system of polyphase brushes can be applied without the above mentioned limitation.

In Figure 1 the control of the speed of the auxiliary dynamo 7 is obtained through the regulator current traversing, after amplification, the armature of the auxiliary dynamo 7 while on Figure 2 the same result is obtained through the regulator current traversing, after amplification. the field winding of the auxiliary dynamo l.

I claim:

1. A power system comprising induction motor including a pair of polyphase windings, a circuit including a regulator dynamo coupled to said induction motor and adapted to create a cur: rent in said circuit varying rapidly with slight variation from a predetermined speed of said induction motor, rotatable means for providing polyphase currents having a frequency deter mined by the rotational speed thereof, cornprising a generator including a field inductor, an armature associated with a commutator rotatable with respect to said field inductor a polyphase system of brushes rotatable about commutator for collecting a polyphase system of currents having a frequency determined by the relative motion between said system of brushes and said field inductor, an electric motor for rotating said system of brushes, means for amplifying the current of said circuit and for supplying said amplified current to said electric motor for controlling the speed thereof, said generator being connected in circuit with one of said polyphase windings of said induction motor, the other of said polyphase windings of said induction motor being adapted to be energized by a polyphase network.

2. A power system comprising an induction motor including a pair of polyphase windings, a regulator dynamo having a shunt excitation winding and an unsaturated magnetic circuit, said regulator dynamo being mechanically coupled to said motor for providing a control current changing with a slight variation from a predetermined speed of said motor, rotatable means for providing polyphase currents having a frequency determined by the rotational speed thereof, an electric motor for rotating said rotatable means, rotatable dynamo electric amplifying means mechanically coupled to said induction motor for amplifying said control current and supplying the amplified current to said electric motor for controlling the speed thereof, said polyphase current providing means being connected in circuit with one of said pair of polyphase windings, the other of said pair of polyphase windings being adapted to be energized by a polyphase network.

3. A power system as in claim 2, wherein said electric motor comprises an armature, and said amplifying dynamo electric means comprises an armature provided with a pair of short circuited primary brushes, a pair of secondary brushes in circuit with said electric motor armature and a stator winding in circuit with said regulator dynamo.

l. A power system as in claim 2 and further including a second rotatable amplifying dynamo electric means mechanically coupled to said induction motor for amplifying the polyphase currents supplied by said first mentioned rotatable means and supplying said amplified polyphase currents to said one polyphase winding.

5. A power system as in claim 2 and further including means for regulating the resistance of the excitation winding of said regulator dynamo.

6. A power system as in claim 2 wherein said regulator dynamo comprises an armature provided with a pair of brushes in circuit with said excitation winding and a second pair of brushes in circuit with said amplifying means.

7. A power system as in claim 2, wherein said electric motor comprises a field winding, and said amplifying dynamo electric means comprises an armature provided with a pair of short circuited primary brushes, a pair of secondary brushes in circuit with the field winding of said electric motor and a stator winding in circuit with said regulator dynamo.

8. A power system comprising an induction motor including a pair of polyphase windings, a regulator dynamo coupled to said motor for providing a control current varying rapidly with a slight variation from a predetermined speed of said motor, means for providing polyphase currents having a frequency determined by the rotational speed thereof comprising a closed circuit resistor, and a plurality of polyphase contact members rotatably related thereto, an electric motor for rotating said contact members, means for amplifying said control current and supplying said amplified current to said electric motor for controlling the speed thereof, a direct current source, means for connecting said direct current source to said resistor at preselected points thereof, means for connecting the output of said polyphase current providing means to one of said pair of polyphase windings, the other of said pair of polyphase windings being adapted to be energized by a polyphase network.

JOSEPH MAXIMUS PESTARINI.

References Cited in the file of this patent UNITED STATES PATENTS Number 

